Embodiment
In illustrative embodiment, MEMS microphone wafer has diaphragm support cylinder substantially to reduce diaphragm sagging (sagging).Correspondingly, this type of embodiment can increase diaphragm area, thereby advantageously increases signal to noise ratio.In order to ensure even meticulousr resolution, this type of embodiment is used spring that diaphragm is connected to 1) supporting cylinder, 2) stationary part of microphone wafer, or 3) be connected to supporting cylinder and stationary part.Below discuss the details of illustrative embodiment.
Figure 1A schematic form illustrates the top perspective view of the microphone 10 of encapsulation, and the microphone 10 of encapsulation can be incorporated to according to the MEMS microphone wafer 16(of illustrative embodiment configuration of the present invention as shown in other accompanying drawing of Fig. 1 C, Fig. 1 D and Fig. 2 and below discussion).In a corresponding way, Figure 1B illustrates the bottom perspective view of the microphone 10 of identical encapsulation in schematic form.
The microphone 10 of these encapsulation shown in the drawings has package substrates 12, package substrates 12 forms interior chamber together with corresponding top cover 14, this interior chamber comprises microphone chip 16, and comprises if necessary independent microphone circuit chip 18(wafer 16 and 18 and all in Fig. 1 C and Fig. 1 D and the accompanying drawing below discussed, illustrated in schematic form).Top cover 14 in the present embodiment is cavate top covers, and it has from the substantially vertical extension of inside top surface to form four wall portions of cavity.In illustrative embodiment, top cover 14 is formed by metal or other conductor material to be microphone wafer 16 shield electromagnetic interference.Top cover 14 is fastened to the top surface of flat in fact package substrates 12 to form interior chamber.
Top cover 14 also has audio input port 20, and audio input port 20 can enter in chamber audio signal.But in alternative, audio port 20 is positioned at another position, as one of them of the sidewall through package substrates 12 or top cover 14.The audio signal and the microphone chip 16 that enter interior chamber interact to produce the signal of telecommunication, and this signal of telecommunication for example, produces the output earcon corresponding with input earcon by additional (outside) assembly (, loud speaker and accessory circuit).
Figure 1B illustrates the lower surface 22 of package substrates 12, and it has for by microphone wafer 16 and substrate, as printed circuit board (PCB) or other electrical interconnection arrangement with electric mode (with in the use of many expections with physics mode) a plurality of contacts 24 of being connected.The microphone 10 of encapsulation can be in far-ranging any application.For example, the microphone 10 of encapsulation can be combined with mobile phone, landline telephone, computer equipment, video-game, hearing aids, hearing instrument, biometric security system, two-way radio, announcement systems (public announcement) and the miscellaneous equipment of switching signal.In fact, can expect that the microphone 10 encapsulating can be as produced the loud speaker of earcon by the signal of telecommunication.
In illustrative embodiment, the package substrates 12 shown in Figure 1A and Figure 1B can be printed circuit board material, as FR-4 or preforming lead frame formula encapsulation (also referred to as " preforming package ").Other embodiment can be used different encapsulated types, for example, and the encapsulation of ceramic chamber.Therefore, the encapsulation of discussion particular type only for illustration purposes.
Fig. 1 C illustrates the sectional view through the microphone 10 of the encapsulation of the straight line C-C of Figure 1A in schematic form.As shown in the figure with mentioned above, substrate 12 and top cover 14 are formed for comprising MEMS microphone wafer 16 and for controlling and drive the interior chamber of mentioning of the electronic component 18 of microphone wafer 16.In illustrative embodiment, electronic component is as the second independent integrated circuit, as application-specific integrated circuit (ASIC) (" ASIC 18 ") is realized.But other embodiment can form MEMS micro-structural and electronic circuit on single wafer.
Bonding or another mechanism that is connected is fastened to substrate 12 by microphone wafer 16 and ASIC wafer 18.Bonding wire is electrically connected to microphone wafer 16 and ASIC wafer 18 the contact weld pad (not shown) of package substrates 12 inside.
Although Figure 1A-1C illustrates the microphone design of top port encapsulation, some embodiment are positioned input port for other position, as passed substrate 12.For example, Fig. 1 D illustrates the sectional view of the microphone 10 of similar encapsulation in schematic form, and wherein microphone wafer 16 covers input port, produces thus large rear end volume.Other embodiment (not shown) is positioned to make it not cover the input port 20 through substrate 12 microphone wafer 16.
Discuss the microphone of special package only for illustration purposes.The microphone 10 of the encapsulation of therefore, discussing in conjunction with Figure 1A-1D is not intended to limit all embodiment of the present invention.
Fig. 2 illustrates the MEMS microphone wafer 16(that can manufacture according to illustrative embodiment of the present invention in schematic form also referred to as " microphone chip 16 ") top perspective view.Subsequent figure 3A-6 illustrates in multiple different embodiment identical microphone wafer 16 through top view and cross section Figure 18 of the straight line 2-2 of Fig. 2.
Except other, microphone wafer 16 also comprises stationary part 26, and stationary part 26 supports and form the variable capacitor 28 with flexible membrane 30.In illustrative embodiment, stationary part 26 comprises backboard 32(and discusses as shown in subsequent drawings and below), backboard 32 for example, is formed by the layer of monocrystalline silicon (the silicon-on-insulator wafer top layer of, below discussing) and other deposition, and diaphragm 30 is only by the material depositing, as the polysilicon of deposition forms.But other embodiment forms stationary part 26 and diaphragm 30 with the material of other type.For example, the material of monocrystalline silicon body material wafer and/or certain deposition can form stationary part 26.In a similar manner, monocrystalline silicon body material wafer, a part for silicon-on-insulator wafer or the material of certain other deposition can form diaphragm 30.
Spring 34 is removable and integrally the outer peripheral edges of diaphragm 30 are connected to the stationary part 26 of microphone wafer 16.Spring 34 forms a plurality of openings 36 that allow at least a portion of audio frequency/voice signal to pass through diaphragm 30 effectively.These openings 36 also can be called " diaphragm openings 36 ", can be by application any shapes that is required to be, and as seam shape, circular hole shape or certain is irregularly shaped.Electric contact 25 on wafer 16 and 18 top surface is provided for the electrical connection of the bonding wire shown in Fig. 1 C and Fig. 1 D.
Fig. 3 A and Fig. 3 B illustrate the more details of the MEMS microphone wafer 16 of this embodiment, but have the diaphragm 30 that is generally rectangle.Specifically, Fig. 3 A illustrates the more details of the top view of the microphone wafer 16 shown in Fig. 2 in schematic form.Fig. 3 B illustrates the sectional view of identical microphone wafer 16 in schematic form.
As best illustrating in Fig. 3 B, the stationary part 26 of microphone wafer 16 has backboard 32, and backboard 32 forms variable capacitor 28 together with diaphragm 30.As well known to a person skilled in the art, variable capacitor 28 produces the signal of telecommunication that represents to incide the input audio signal on diaphragm 30.In order to be beneficial to operation, backboard 32 has a plurality of open-work openings (" backboard opening 38 ") of introducing dorsal cavity 40.Opening 38 can be made as shape, size and configuration to make performance optimization.A kind of this type of configuration has hole and gap (that is, elongated hole) of circular, and another kind of configuration only has the hole of the circular of arranging by AD HOC.
When static, no matter whether energy supply, the diaphragm of many prior aries for example, because inherent strain and earth gravity all can be out of shape (, they may sink except other) to a certain degree.A plurality of parts of some prior art diaphragms may be sunk, its scope between " nominal range/gap 42 " between itself and backboard 32 25 and 50% between.More definite, " nominal range/gap 42 " is interpreted as in the situation that diaphragm 30 is completely smooth to distance when static between diaphragm 30 and backboard 32.For example, the some parts of diaphragm 30 may be with backboard 32 spaced apart approximately 3 microns, and the region more placed in the middle of diaphragm 30 may be with backboard 32 spaced apart approximately 2 microns.
Sink and increased diaphragm 30 by the possibility of contact backboard 32, thereby may cause a large amount of problems.For example, diaphragm 30 may be adhered in backboard 32(this area and be called " viscous "), this may damage equipment or cause diaphragm 30 and backboard 32 between short circuit.Even if these problems of mentioning do not occur, between diaphragm 30 and backboard, contact the quality that for example, reduces output signal except also usually making signal peak distortion (, scabbling signal peak) other situation.
For example, in some microphone design of unusual Small diaphragm-piece (, the longest dimension parallel with the X-Y plane of Fig. 3 A is less than approximately 1 millimeter), it may not be problem that diaphragm sink.But inventor recognizes that less microphone usually has the signal to noise ratio that larger diaphragm is low.Often the larger diaphragm of expectation improves microphone property thus.For example, if can control saggingly, have and be greater than the signal to noise ratio that the maximum sized diaphragm of 1 millimeter should obtain raising.
Therefore, in order to control diaphragm, sink, illustrative embodiment of the present invention, as described in Fig. 2, Fig. 3 A and Fig. 3 B, has at least one supporting cylinder 44 of the interior section of supporting diaphragm 30.In other words, supporting cylinder 44 solidifies a part for diaphragm 30 effectively, thereby makes it static in fact.This often approaches approximate centre or the barycenter of diaphragm 30.For example, cylinder 44 can be positioned between two opposite edges of diaphragm 30 equidistant in fact.Although be sure of that various embodiments has produced in conjunction with larger diaphragm (that is, being greater than approximately 1 millimeter) effect of improving, various embodiments is also applicable to compared with Small diaphragm-piece.
As mentioned above, spring 34 by with stationary part 26 in conjunction with the periphery that carrys out support membrane 30.These springs 34 shown in Fig. 3 A and Fig. 3 B form spring opening mentioned above or space 36.Therefore, the some parts of the periphery of diaphragm 30 is not directly connected with stationary part 26.Fig. 3 A is called vocabulary " not supporting part " by a part of periphery.In any situation, diaphragm periphery a plurality of points around are all supported.Therefore,, although there is the unsettled situation of the some parts of periphery, this arranges and is not considered as cantilevered construction.
For example, diaphragm periphery can be at least every 180 degree or littlely there are a plurality of districts and be connected (that is, the subtend spring 34 in every side of diaphragm 30) with spring 34.Other embodiment can have by approximately 120 degree or less, approximately 90 degree or less, approximately 60 degree or less, approximately 45 degree or the less springs of uniformly-spaced opening 34.
The diaphragm 30 of rectangular design as shown in Figure 3A has 16 springs 34, these 16 springs 34 in fact equi-spaced apart ground round diaphragm periphery.As rectangle diaphragm 30, these 16 springs 34 without as diaphragm 30, be accurate circular and equidistant from distance around diaphragm 30.On the contrary, locate them into and make them between it, have at least two subtend spring 34(, approximately 180 degree separate) and other.Therefore, the diaphragm 30 of this rectangular design can be considered as having the spring 34 that approximately 180 degree and less spacing separate.The another kind of mode of understanding this diaphragm 30 is that it has a plurality of straight lines, and each limit has at least one spring.Therefore, if diaphragm 30 is another kind of polygonal shapes, as octagon, pentagon etc.., it on each limit, have at least one spring 34 and, be not cantilever type thus.Each limit can have the spring 34 of identical quantity, type and spacing, or the spring 34 of different rates, type and spacing.If diaphragm 30 is irregularly shaped designs, can expects and at least make spring 34 interval 180 degree that gratifying effect will be provided.
Spring 34 around diaphragm periphery in Fig. 3 A and Fig. 3 B is that elongation and spiral fashion form.As well known to a person skilled in the art, coil spring 34 can provide more multi-control than 34 pairs of diaphragms 30 of the short and thick spring of direct straight line.Certainly, the spring 34 of other type should meet the demands, as being only secured to stationary part 26(, as drum) spring 34.Thereby such spring 34 is thinner allow larger diaphragm flexible and be designed to allow diaphragm 30 more as the indentation (depression) (seeing following) of piston.In addition,, although the microphone wafer 16 of Fig. 3 A has the spring 34 of symmetrical location, alternative can have the spring 34 of asymmetrical positioned.
This is to contrast with some prior art design formings, and it can only be fastened to a side of supporting cylinder 44 or stationary part 26.Definitely, not to connect diaphragm periphery, the outer peripheral edges of the actual permission of the design diaphragm 30 of some prior aries hang with cantilever type form.Inventor recognizes the effect that this type of prior art design is more owed controllability and often caused difference.Illustrative embodiment should have more controllability than mentioned prior art design in Z direction so that more plane is more round mobile to backboard 32 as the mode of piston.
For this reason, spring 34 can also be combined between supporting cylinder 44 and the inner peripheral of diaphragm 30 to further improve performance.No matter what's the matter, these springs 34 can be in type discussed above any, and there is the not supporting area that produces space 36 between cylinder 44 and diaphragm 30 or spring 34.Similar with outer peripheral edges spring 34, these contained springs 34 can for example, around supporting cylinder 44 180 degree or less and (locate, 120 degree or less, 90 degree or less, as shown in Figure 3A etc.), or for example, locate with the alternate manner above discussed in conjunction with external springs 34 (, thering is a spring in each side of cylinder 44 of polygon cross section).Other embodiment is not used spring (as discussed below) between cylinder 44 and diaphragm 30.
As proposed above, cylinder 44 can have any Number Forms, shape and size.For example, cylinder 44 can have essentially rectangular, circle or irregular shape of cross section.In illustrative embodiment, cylinder 44 is made by polysilicon, and globality ground extends also and is connected with backboard 32 to globality from diaphragm 30.This type of connection can be to be considered as the permanent connection (that is, there is no unconventional active force, as used in the situation of saw, these assemblies will connect always) of a type.Be different from the non-MEMS microphone of some prior art, cylinder 44 does not conduct electricity with diaphragm 30.On the contrary, cylinder 44 essence are electric end end (dead end).
Therefore, cylinder 44 is not electrically connected to diaphragm 30 and backboard 32, is because if like this, and two of variable capacitor 28 pole plates (that is, backboard 32 and diaphragm 30) will be same potential, thereby cause capacitor to work.For this reason, spring 44 preferably itself and diaphragm 30 and backboard 32 one of them or the two between there is certain insulating material.For example, in manufacture process, before deposited film lamella, technique can for example, at the upper insulating oxide (, natural oxide) that forms in the top side of cylinder 44 (that is the side that, cylinder 44 is finally connected with diaphragm 30).Thus subsequent fabrication steps can be on this oxide deposit spathic silicon membrane layer.Oxide layer between the top of cylinder 44 and diaphragm 30 stops between diaphragm 30 and backboard 32 telecommunication via cylinder 44 thus.
Certainly, MEMS diaphragm wafer 16 can have for by other parts of one of them or the two electric insulation of cylinder 44 and diaphragm 30 and backboard 32.Another kind of technology can form oxide layer or insulating barrier between cylinder 44 bottoms in backboard 32.One of them or the two the region that other embodiment can be connected to diaphragm 30 and backboard 32 around it around cylinder 44 forms electric insulation groove.Other embodiment can utilize non-conductive material to form cylinder 44 simply, for example, and conventional conduction or certain combination of electrically non-conductive material in the silicon that undopes, oxide, nitride or MEMS manufacturing process.
Although Fig. 3 A and Fig. 3 B illustrate the spring 34 all having along inner peripheral and the outer peripheral edges of diaphragm 30, other embodiment can be from these regions arbitrary region or the two omit spring 34.Fig. 4 A and Fig. 4 B illustrate an embodiment in schematic form, and the former is plane graph, and the latter is cross-sectional perspective view.This embodiment retains the spring 34 along outer peripheral edges, and cancels the spring 34 between cylinder 44 and diaphragm 30.Other embodiment can only have the spring 34 along interior diaphragm periphery, or all there is no spring 34 along inner or outer diaphragm periphery.Fig. 4 B illustrates indentation (respectively having three or four parts from approximate centerpoint projection) corresponding with the opening 38 that passes backboard 32 on diaphragm 30 by way of parenthesis.
As a plurality of beneficial effects, use cylinder 44 or other parts to make the substantial middle region of diaphragm 30 keep static in fact.Definitely, it shortens the length/span of diaphragm 30 significantly.For example, consider the circular film of 1 mm dia, its conventionally therein heart place sink, through 3 microns of gap 42(of nominal, if completely smooth, the gap 42 between diaphragm 30 and backboard 32 will be 3 microns) approximately 1 micron.Should sink diaphragm to reduce approximately 50% in the center that cylinder 44 is positioned to about diaphragm 30.Therefore, should be unable to sink is greater than approximately 0.5 micron to all the other moveable parts of diaphragm 30 (that is, not kept static in fact part by cylinder 44).
Inventor recognizes that the sagging minimizing of this diaphragm makes them can increase diaphragm 30, thereby increases the signal that variable capacitor 28 produces.Therefore, the example above that continues, diaphragm 30 can have the diaphragm 30 that doubles this size now; There is the diameter of approximately 2 millimeters.But, under worst case, can expect that diaphragm 30 sink same approximately 1 micron.But, because area is along with square increase of radius, so this produces the increase of 4 times of surface areas, and produced thus the signal to noise ratio of corresponding 4 times and promoted.
Should note the certain signal of demoting to a certain degree and improving of area that cylinder 44 occupies.But intuition is thought and avoided cylinder so that the surface area of variable capacitor 28 maximizes on the contrary therewith, inventor recognizes that the signal of remarkable improvement substantially surpasses this performance degradation that cylinder causes.In other words, cylinder 44 only produces inapparent hydraulic performance decline or degradation in signal quality.In addition the noise that, variable capacitor 28 produces can not increase corresponding speed with signal and increase.This provides the beneficial effect of the signal to noise ratio that substantially improves microphone wafer 16.
Inventor finds to support cylinder 44 a plurality of fringe benefits is provided.Definitely, those skilled in the art will know that ASIC wafer 16 has the input capacitance that reduces the net signal that the microphone 10 of encapsulation produces.It is minimum or by its minimizing that the substantive microphone wafer electric capacity increasing is reduced to the negative effect of other parasitic capacitance in this input ASCI electric capacity and system thus.In addition, larger microphone wafer electric capacity reduces noise by mobile its effective low-frequency cutoff.
In use procedure, incident sound tone signal roughly moves diaphragm 30 along Z axis.Ideally, diaphragm 30 moves almost all moving up and down with phase same rate in its a plurality of points of – as plunger along Z axis.Spring 34 is configured to guarantee that diaphragm 30 moves in expection mode when receiving the signal with appointment amplitude.For example, some microphone wafer may be for example, to make for short arc voice signal (, not being considered as the signal ringing very much), and thus, has the relatively low spring of spring constant 34.This type of spring 34 can be more carefully, longer, or to allow the mode of this class behavior to make.In fact, very the signal of high amplitude impacts this type of microphone and may damage spring 34 and diaphragm 30.
Although be discussed as the roughly barycenter or the center that roughly approach or be positioned at diaphragm 30, some embodiment (as mentioned above) may make cylinder 44 be offset to other position with respect to diaphragm 30.Fig. 5 illustrates another embodiment that microphone wafer 16 wherein has a plurality of cylinders 44 in schematic form.These cylinders 44 can and should be used for strategically locating according to the desired use of microphone chip 16.Those skilled in the art can select applicable position according to the purposes of expection.
Other embodiment has removable cylinder 44 between diaphragm 30 and backboard 32.Fig. 6 A and Fig. 6 B illustrate this type of embodiment, and wherein cylinder 44 globality ground extend, from diaphragm 30 projections.As shown in Figure 6A, the position of energy supply, diaphragm 30 are not biased conventionally, so that cylinder 44 does not contact backboard 32, when microphone chip 16 is not during by energy supply.Cylinder 44 can extend the whole length in diaphragm 30/ backboard 32 gaps 42 in fact, and only leaves little space for advancing when receiving voltage.For example, while using in the microphone chip 16 between diaphragm 30 and backboard 32 with 3 microns of gaps 42 of nominal, cylinder 44 can extend make it when energy supply not apart from only approximately 0.1 or 0.2 micron of backboard 32.This distance is not by nominal, energy supply sagging included consideration in yet.Other embodiment can allow cylinder 44 even when energy supply not, to cross over whole diaphragm 30/ backboard 32 gaps 42.
This sectional view that should note Fig. 6 A is that the spring 34(in cross-film sheet 30 left sides is from accompanying drawing visual angle) and the open space 36 on diaphragm 30 right sides.In other words, this embodiment spring structure around may be combined any one structural similarity in those structures that other embodiment describes above.
Between the diaphragm 30 of Fig. 6 A and backboard 32, apply electrostatic force (for example, the power that voltage difference causes) and force diaphragm 30 downward, until cylinder 44 touches backboard 32(Fig. 6 B).Point at this moment, microphone wafer 16 is ready, prepares to receive and the voice signal of conversion input.
From diaphragm 30, do not extend, but the alternative of the microphone chip 16 shown in Fig. 6 A and Fig. 6 B makes cylinder 44 extend upward from backboard 32.So in some sense be not as satisfactory like that as the embodiment described in Fig. 6 A and Fig. 6 B, because diaphragm 30 is often much thin than backboard 32, and thus may be impaired and the top of cylinder 44 is applied to too large power.
Fig. 7 illustrates the simplification process of using the MEMS microphone chip 16 shown in Fig. 6 A and Fig. 6 B.This process starts from step 700, wherein to microphone wafer 16 energy supplies.This causes diaphragm 30 and cylinder 44 to move down to touch backboard 32(Fig. 6 B).When energy supply, the part that diaphragm 30 is connected with cylinder 44 globalities should keep static in fact.
Point at this moment, the voice signal (step 702) that MEMS microphone wafer 16 receives and enters at normal processes transfer swap-in.Finally, process is removed energy supply and is ended at step 704 microphone wafer 16.The elasticity of spring 34 and diaphragm 30 makes diaphragm 30 and cylinder 44 turn back to resting position thus, as shown in Figure 6A.
Although above discuss and disclose multiple example embodiment of the present invention, should appear to those skilled in the art and can make under the prerequisite that does not deviate from true scope of the present invention and will realize the multiple modification of advantages more of the present invention.